Improving the performance of Al/NiO Schottky-barrier diodes by inserting an introduced-oxygen MgO layer

Magnesium oxide (MgO) thin film without and with introduced oxygen was inserted between Al and nickel oxide (NiO) via a sputtering method to improve the performance of Al/NiO Schottky barrier diodes (SBDs). The SBDs without MgO insertion, Al/NiO, revealed a non-rectifying I-V curve. SBDs with MgO insertion, Al/MgO/NiO, significantly suppressed the leakage current. However, the Al/MgO/NiO SBDs without the introduced-oxygen MgO still exhibited a non-rectifying I-V characteristic. Nevertheless, the Al/MgO/NiO SBDs with the introduced-oxygen MgO reduced the leakage current by approximately 5168 times compared to the Al/NiO SBDs. Simultaneously, the Al/MgO/NiO SBDs with the introduced-oxygen MgO appeared a good rectifying behaviour having a rectification ratio of 145. A low Schottky-barrier height (SBH) of 0.69 eV was observed in Al/NiO SBDs. After insertion of MgO without introduced oxygen, the SBH was raised to 0.78 eV in Al/MgO/NiO. The SBH was further increased to 0.94 eV in the Al/MgO/NiO SBDs with introduced oxygen. The reason of less leakage current and large SBH in the Al/MgO/NiO SBDs with introduced oxygen is caused by that the compensated defects in MgO. The introduced oxygen atoms during MgO sputtering compensated for the oxygen vacancies of MgO and hence less defects. A Ln(I) versus Ln(V) plot was used to study carrier transport mechanisms. Only one region of ohmic transport was observed in Al/NiO and Al/MgO/NiO SBDs without introduced oxygen, where holes tunnelled from NiO to Al through the surface defects of NiO and MgO. In contrast, two distinct transport regions were observed in Al/MgO/NiO SBDs with introduced oxygen. For V < 0.8 V, diffusion-tunnelling dominated the transport. However, the trap-free space-charge-limited current controlled the transport at V > 0.8 V; here, the injected holes from NiO occupies most of the MgO traps, and thus hindered the further injection of holes.